Definition

• Normal blood pH is 7.35 to 7.45
• Acidosis is Arterial pH < 7.35. Can be due to metabolic reasons or Respiratory reasons
• Alkalosis is Arterial pH > 7.45. Can be due to Metabolic causes of Respiratory causes

CALCULATION–

Done with the Anion gap formula

Na + K – (Cl + HCO3)

METABOLIC ACIDOSIS

Investigations

• Acidosis on blood gas
• Anion gap  of over 15 OR
• Bicarbonate less than normal (normal 22-28)
• Compensated fall in PaCO2

Causes

Increased Acid production

• Ketoacidosis like diabetic, starvation
• Lactic acidosis- in cardiac arrest, shock. Hypoxia, anemia, loere failure, sepsis, pancreatitis
• Exogenous acid ingestion like Salicylate, Menthol, Ethylene glycol

Decreased acid production

• Renal failure

Loss of alkali

• Diarrhoea
• Small bowel fistulas

Decreased hydrogen ion excretion

• Hyperaldosteronism
• Distal renal tubular acidosis

Metabolic acidosis with normal anion gap causes

• GI loss of bicarbonate
• Renal tubular acidosis
• Treatment with Carbonic anhydrase inhibitors

Metabolic acidosis with high anion gap causes

• Renal failure
• Ketoacidosis
• Lactic acidosis
• Salicylate poisoning

Mnemonics for metabolic acidosis

• MUDPILES– Methanol, Uremia, Diabetes, Paraldehyde, Iron/ Isoniazid, Lactate, Ethylene glycol, Salicylate

METABOLIC ALKALOSIS

Investigations

Blood pH > 7.45 and

Plasma bicarbonate > 28 mmol/L

Cause

Hydrogen loss through GI tract

• Vomiting
• High output fistula

Renal hydrogen loss

• Mineralocorticoid loss
• Hypercalcemia
• Posthypercapnic alkalosis
• Diuretics

Syndromes

• Cushing’s syndrome
• Bartter’s syndrome

Gain of bicarbonate

• Excess antacids

RESPIRATORY ACIDOSIS

Investigation

Blood pH < 7.35 and PaCO2 > 42 mmHg

Cause

Acute Respiratory distress due to

• Sedative medications
• Head injury

Neuromuscular disorders like

• GB syndrome
• Myasthenia gravis
• Obesity

Diagnosis

• Blood gas shows acidosis
• Increase in PCo2 above 44 mmHg
• There can be compensatory increase in Bicarbonate

Clinical features

• Confusion
• Bounding pulses
• Coma

MANAGEMENT

• Start oxygen
• Assist ventilation by bag and mask or CPAP or intubations
• Correct underlying disorder

RESPIRATORY ALKALOSIS

Causes

• Asthma
• Pneumonia
• Pulmonary oedema
• Anemia
• Salicylate poisoning
• Pain/ Fear
• Sympathomimetics

Diagnosis

• Blood gas shows alkalosis
• Decrease in PaCo2 below 36 mmHg